Patent GB-882469-A (GB)
Title: Navigation devices for aircraft
Inventor: GRIFFITH ALAN ARNOLD
IPC: G01S1/02
Filed: 1958-10-23
Abstract: 882,469. Radio navigation. ROLLS-ROYCE Ltd. Oct. 16, 1959 [Oct. 23, 1958], No. 33961/58 Class 40(7). The position of an aircraft in space is determined by measuring on the aircraft the directions of at least three spaced ground radio beacons of known location transmitting characteristic signals. The invention is described as applied to a system for assisting the landing of vertical take-off aircraft. As shown in Fig. 1 four beacons transmitting different radio frequencies or pulse modulations are located at the corners of a rectangle ABCD symmetrically enclosing a rectangular landing pad 7 and four directional aerials a, b, c, d on the aircraft 1 are automatically directed at the beacons A, B, C, D respectively, the angles between the directional axes of the aerials a, b, c, d and the vertical plane 8 through the longitudinal axis of the aircraft 1 being indicated by α1, α2, α3 and α4 respectively. As shown in Figs. 2 and 3 the aerial a and b are mounted under the aircraft on a rectangular frame 3 which is rotatable about a horizontal axis 5 perpendicular to the longitudinal axis of the aircraft, the directional axes of the aerials a and b being rotatable in a plane perpendicular to the frame 3 about axes which are spaced along and perpendicular to the frame axis 5. Each aerial system may comprise a conventional conical scan or static overlapping beam arrangement producing "horizontal" and "vertical" components of the misalignment error between the directional axis of the aerial and the line of sight to the corresponding transmitter, the two vertical error signals being combined to control the angular position of the frame 3 about its horizontal axis 5 and each "horizontal" error signal being used to control the angular position of the corresponding aerial directional axis in the plane perpendicular to the frame 3. The aerials c and d are mounted in a similar manner in a frame 4, Fig. 2, having a horizontal axis 6 parallel to the axis 5 of the frame 3. In operation the aircraft is manoeuvred until α1 = α2 and α3 = α4 and in this position the vertical plane 8 through the longitudinal axis of the aircraft bisects the sides AB and CD of the rectangle ABCD at points E and F, the angle # subtended at the aircraft by the points E and F being equal to the angle between the frames 3 and 4. A desired landing path may be specified by defining the quantities #, d#/dt and d(α1 + α2)/dt or d(α3 + α4)/dt  as functions of a prescribed variation of (α1 +α2) or (α3+α4) and corresponding values of these quantities for a standard landing path are stored on cams or magnetic tape which are driven in accordance with the prescribed variation of (α1+α2) or (α3+α4). These recorded values are compared with corresponding observed values to give corresponding error signals which are converted into appropriate control signals, e.g. for controlling the magnitude and direction of the jet thrust in a jetlift aircraft, by multiplying by suitable coefficients which may be stored on additional cams if they are functions of (α1+α2) or (α3+α4). The resultant control signals may be applied to an automatic pilot or to a flight direction indicator. Normally quantities which are a function of (α1+α2) are employed but, since the position of the aircraft is completely defined by any three of the angles α1..α4, if either of the aerials a, b fails to lock on to its transmitter the control may be transferred to the quantities dependent on (α3+α4). Alternatively only three transmitters may be used. If another landing pad is located outside the rectangle ABCD, one side of the landing pad being coincident with the side CA, Fig. 7 (not shown), an aircraft may be landed on said pad by maintaining the ratio of the tangents of α1 and α2, or α3 and α4 constant at a value appropriate to the position of the landing path relative to the rectangle ABCD. In another embodiment the four aerials a..d are independently mounted so that each aerial can always lock on to its respective transmitter. The resultant angle data is fed to a computer, Fig. 4 (not shown), which produces signals representing the height of the aircraft, the distance of the aircraft from the landing pad, its pitch, roll and yaw together with the rates of change thereof and also the speed of the aircraft and its angle of descent. These signals are then compared with corresponding demand signals which are varied in time manually or automatically, Figs. 5 and 6 (not shown), in accordance with a desired landing procedure to give corresponding error signals.